Conventionally, a variety of conveying apparatus for conveying a workpiece between press machines or the like have been proposed.
For example, there is a workpiece conveying apparatus including a crossbar unit extending in a direction substantially orthogonal to a workpiece conveying direction. In such an apparatus, for example, as described in Japanese Patent Application Laid-open No. Hei 04-238633 (hereinafter, referred to as Patent Document 1), a crossbar 2 (refer to reference symbol 2 in Patent Document 1) is disposed so as to transversely cross the workpiece conveying direction and is reciprocated in the workpiece conveying direction and the direction opposite to the same. The crossbar 2 has a workpiece gripper attachment 4 (refer to reference symbol 4 in Patent Document 1) mounted thereto, for holding and releasing a workpiece by vacuum adsorption, magnetic adsorption, or the like
Note that, a plurality of kinds of such workpiece gripper attachments are prepared in accordance with sizes or shapes of workpieces, and during preparatory work, there is performed an operation of replacing a workpiece gripper attachment with another workpiece gripper attachment to be used in accordance with the workpiece.
Here, there is supposed a case where such replacement operations of workpiece gripper attachments are manually performed during the preparatory work. For example, in the apparatus described in Patent Document 1, two locking mechanisms 20 (refer to reference symbol 20 in Patent Document 1) are provided to a single workpiece gripper attachment 4, and each of these locking mechanisms 20 includes two lock pins 22 (refer to reference symbol 22 in Patent Document 1). Accordingly, when the workpiece gripper attachment 4 is to be mounted to or removed from the crossbar 2, operations of simultaneously removing four lock pins 22 from tapered holes 15 (refer to reference symbol 15 in Patent Document 1) are required, and hence two or more workers may be required to perform the operations.
Therefore, when the replacement operations of workpiece gripper attachments are manually performed in the apparatus described in Patent Document 1, the working efficiency is actually deteriorated.
Note that, when the replacement operations of workpiece gripper attachments are to be automatically performed, the following configuration is required. For example, in the apparatus described in Patent Document 1, as described above, two locking mechanisms 20 are provided to a single workpiece gripper attachment 4, and each of the locking mechanisms 20 includes two lock pins 22. Accordingly, when the workpiece gripper attachment 4 is to be mounted to or removed from the crossbar 2, the operations of simultaneously removing four lock pins 22 from the tapered holes 15 are required.
Therefore, in the apparatus described in Patent Document 1, it is required to provide a plurality of unlocking cylinders 30 (actuators) for removing the lock pins 22 from the tapered holes 15, to a receiving member 26 (refer to reference symbol 26 in Patent Document 1) for supporting a workpiece gripper attachment 4 not to be used. When such a plurality of unlocking cylinders 30 (actuators) are provided, the apparatus configuration may become complicated, the weight and size may become larger, and the cost may increase.
In the apparatus described in Patent Document 1, the workpiece gripper attachment 4 includes a pair of locking mechanisms 20, which each includes two lock pins 22, and hence the weight may increase.
Note that, there is a demand for speeding up the conveying speed of the workpiece, and also speeding up the press working (improvement of productivity). Accordingly, a crossbar having a workpiece gripper attachment mounted thereon is reciprocated between press machines with relatively high speed, and hence the weight of the workpiece gripper attachment is desired to be reduced as much as possible. When the weight of the workpiece gripper attachment increases, speedup of the conveying speed of the workpiece (reciprocating speed of crossbar) causes large vibrations or the like due to its large inertial force. Accordingly, the workpiece conveying speed cannot be actually increased beyond a predetermined level.